This invention relates to austenitic stainless steels having improved mechanical properties at low temperature service. More particularly, the invention relates to stable austenitic Cr-Ni-Mn steels having good strength, fabricability, including welding, and suitable for low temperature service.
It is known to use austenitic stainless steel for structures used in low temperature and cryogenic applications where corrosion resistance is likewise significant. In these applications, in addition to austenitic stainless steels, it is known to use aluminum alloys or 9% nickel-containing alloy steels. The latter material has the advantage over austenitic stainless steels in that it exhibits relatively higher strengths and therefore can be used in reduced section thicknesses. The advantage of aluminum alloys are the lightweight and good strength/weight ratios. These materials, however, are deficient in both corrosion resistance and fabricability relative to austenitic stainless steels. Applications include construction of vessels, such as pressure vessels, which include welding as an essential fabrication step for use in low temperature service. Welding of austenitic steels may result in sensitization, i.e., carbide precipitation, which is deleterious to the welded vessels when in service.
What is needed is an austenitic stainless steel having lower cost alloying elements, particularly lower nickel content which is relatively expensive, but exhibiting mechanical strength and low temperature properties comparable to higher nickel-containing alloys.
It is, accordingly, a primary object of the present invention to provide an austenitic stainless steel having high room temperature strength with good low temperature properties, particularly strength and fabricability, along with corrosion resistance and resistance to sensitization to permit fabrication as by welding.
This and other objects of the invention, as well as a more complete understanding thereof, may be obtained from the following description and specific examples.